A. Field of the Invention
The present invention relates to machines and apparatus for making ultrasonic wire bonds on miniature workpieces such as microcircuits and read/write heads of the type used to read data from and write data to disk memories. More particularly, the invention relates to an automatic ultrasonic bonding machine that includes an orbital head rotatable by a motor drive, thus enabling an ultrasonic wedge-type wire bonding tool protruding from the head to be oriented in arbitrary azimuthal directions, thereby enabling wire to be paid out without twisting through a wire feed bore disposed diagonally through the bonding tool, from a first bond site to subsequent bond sites located at arbitrary compass directions from the first bond site, without requiring that the workpiece be rotated.
B. Description of Background Art
Miniature electronic circuits, or xe2x80x9cmicro-circuits,xe2x80x9d are used in vast quantities, in a wide variety of consumer, commercial, industrial and military devices and equipment. The majority of such micro-circuits are of a type referred to as integrated circuits. Integrated circuits contain a number of active circuit elements such as transistors, and passive elements such as resistors and capacitors. In semiconductor integrated circuits, conductive paths between circuit elements on a semiconductor substrate are formed by selectively etching the substrate. In hybrid micro-circuits, circuit elements mounted on a ceramic substrate are usually interconnected by conductive ink paths on the substrate.
The functional portions of integrated circuits are typically in the form of very small, rectangular-shaped chips, ranging in size from 0.025 inch to 0.200 inch or more on a side. Input connections to integrated circuit chips are often made by bonding a very fine wire to conductive pads on the chips, the other end of each wire being bonded to a conductive terminal that is sufficiently large and robust to be inserted into a printed circuit board and soldered to conductors on the board. Wire bonding of this type utilizes ultrasonic energy and/or heat to form an intermetallic bond or weld between the wire and metallic bond site. Such wire bonds are also used to form interconnections between pads of integrated circuits, and to connect lead-out terminals to delicate read/write heads used in disk memories.
Typically, bonding wires used to interconnect the pads of a semiconductor chip to terminals of a package containing the chip are made of aluminum or gold, and have a diameter of about 1 mil (0.001 inch). Those wires must be bonded to small, typically rectangular-shaped, integrated circuit pads a few mils wide.
The most common method of interconnecting wires between semiconductor chip pads and external terminals is to form an ultrasonic weld at each end of a conducting wire. To form such bonds, the free end of a length of bonding wire is placed in contact with a pad. Then the tip of an ultrasonic transducer is pressed against the wire, and energized with ultrasonic energy for a short time interval, welding an end of the wire to the pad. The free end of the bonded wire is then moved to other pads, and bonded thereto by the same process. After the last bond in a series of bonds has been thus formed, the wire is severed near the last bond.
In view of the very small size of the micro-circuit pads and bonding wire, it can be appreciated that ultrasonic bonding of connecting wires to integrated circuit pads must be performed using a tool mounted in a bonding machine that permits the tool to be manipulated to precisely controllable positions within a work area containing a workpiece.
Typical wire bonding machines used for ultrasonic welding of wires to micro-circuit pads includes an elongated, generally vertically disposed, force-applying member or xe2x80x9ctool.xe2x80x9d The tool is connected at the upper end thereof to a source of ultrasonic energy, such as a piezoelectric transducer connected to an electrical energy source alternating at an ultrasonic frequency. Usually, the tool is connected to the transducer through a tapered horn structure that matches the acoustic input impedance of the tool to the output impedance of the transducer, which typically has a larger diameter than the tool.
One type of ultrasonic bonding tool used to bond wires to micro-circuit pads is referred to as a wedge bonder and has a flat lower working face adapted to press a bonding wire into contact with a pad, while ultrasonic energy is applied through the tool to the wire to form an ultrasonic weld. This working face is usually quite small, typically having a rectangular shape only about a few mils on a side, to permit bonding wire to small micro-circuit pads, without contacting adjacent circuit elements. Typically, this is done by first viewing a particular workpiece pad and tool tip in a stereo microscope and video camera to align a workpiece relative to a bonding machine, and then using an automatic actuator system to position the tool tip at consecutive bond site locations on the workpiece, using a control system which employs pattern recognition logic.
In most wire bonding machines, the bonding tool is so constructed as to facilitate the positioning of bonding wire over a pad, prior to performing the bonding operation. Such bonding tools may include an upwardly angled lower face rearward of the working face, and a generally vertically disposed rear face. An angled bore or wire guide hole having an entrance aperture in the rear face and an exit aperture in the angled lower face of the tool enables bonding wire supplied from a reel mounted upwardly and rearwardly of the tool to be paid out through the exit aperture in the angled lower face of the tool. Typically, a remotely actuable clamp located rearward of the wire guide hole entrance and movable with the tool is used to feed bonding wire through the guide hole.
The clamp used to push wire through the guide hole of a bonding tool usually consists of a pair of jaws that may alternately be closed to grip the wire, and opened to allow free travel of the wire. Generally, such clamps may be moved toward and away from the guide hole entrance, typically on a line of movement which coincides with the axis of the guide hole. To feed wire through the guide hole, the jaws of the clamp are first opened, and the clamp then moved away from the guide opened, and the clamp then moved away from the guide hole. The jaws are then closed to grip the wire, and then moved towards the guide hole, thus feeding wire through the guide hole.
In wire bonding machines of the type just described, the machine is used to translate the bonding tool to the proper position to bond wire to a first bond site of a pair of bond sites, such as a pad on an integrated circuit die, feed wire out through the guide hole exit aperture, move the tool to a second bond site and form another bond. In this manner, any desired number of pads or other elements of a circuit can be connected together, in a procedure referred to a xe2x80x9cstitchxe2x80x9d bonding. After the last bond in a series of bonds has been made, the wire must be severed, to permit making bonds between other pairs of bond sites. Oftentimes, the bonding tool itself is utilized to sever the bonding wire.
In moving a wedge bonding tool from a first bond site to a second bond site, the tool must be translated rearward from, the first site to the second site, in a vertical plane containing both the longitudinal axis and wire-guide bore axis of the tool. This requirement results from the fact that wire paying out forwardly through the exit aperture of the bonding tool tip must remain in the plane containing the longitudinal and guide hole axes of the tool, to ensure that the wire will not bind on the exit aperture chamfer, or become twisted.
Because of the requirement for translating a wedge bonding tool from a first to subsequent bond sites in the plane of the bonding tool longitudinal axis and wire guide bore axis, existing wedge bonding methods require that a workpiece be rotated to align a direction vector between the two sites with the bonding tool plane, and subsequent translation of the bonding tool rearwardly in that plane along the direction vector.
One method of performing the required relative translations and rotations of a wedge bonding tool relative to a workpiece utilizes a support platform for the workpiece, which is translatable in an X-Y plane perpendicular to the longitudinal axis of the bonding tool, and rotatable in the Yxe2x80x94Y plane. With this method, the bonding tool need only be translatable downwardly, in a minus xe2x88x92Z direction to effect a bond, and upwardly in a plus +Z direction after a bond has been made.
In some ultrasonic wire bonding applications, the bonding tool tip may move in arbitrary compass directions between first and succeeding bond sites. Thus, ball bonding tools, which feed bonding wire through a single capillary bore coaxial with the longitudinal axis of the tool may be translated in any direction between bond sites, without regard to the orientation of the tool, because of the azimuthal symmetry of the tool. For such applications, it is possible to translate the bonding tool in X and Y directions, as well as the Z direction, to make bonds between sites on a fixed workpiece. Thus, the present inventor disclosed in copending application, Ser. No. 09/570,196, filed May 12, 2000, an Automatic Ultrasonic Bonding Machine With Vertically Tiered Orthogonally Translatable Tool Support Platforms, which include a positioning mechanism for automatically translating the tip of an ultrasonic bonding tool by drive motors to precisely pre-determinable positions within a three-dimensional coordinate space containing a workpiece. The machine described in that application provides means for translating a bonding tool, in X-Y directions parallel to a plane containing a workpiece to position the tool tip over a particular bond site, translating the tool downwardly in a minus xe2x88x92Z direction to make an ultrasonic wire bond, translating the tool upwardly to withdraw its tip from the first bond site, and translating the tool in X-Y direction to position the tool over a subsequent intended bond site, and form thereat a subsequent bond. Thus, the disclosed machine eliminates the a requirement for a rotatable X-Y table for supporting a workpiece, and provides a highly effective method for making bonds on workpieces located on a conveyor, for example. The present invention was conceived of to further advance the wire bonding machine art, by providing a machine capable of making a sequence of wedge bonds without requiring either rotation or translation of a workpiece.
An object of the present invention is to provide a machine for positioning an ultrasonic wire bonding tool at precisely determinable first bond site locations relative to a workpiece, orbiting the bonding tool about its longitudinal axis to an arbitrary compass direction, and translating the tool in the compass direction to precisely determinable second bond site locations while maintaining the tool irrotational in the plane of translation to the second bond site location, thus allowing a bonding wire to pay out through an aperture through the bonding tool from said first location to said second location without twisting from the translating plane.
Another object of the invention is to provide an ultrasonic wire bonding machine having an orbital head which rotatably supports a wedge bonding tool having a wire feed bore which angles upwardly and rearwardly from the tip of the tool, whereby the head may be rotated to rotate a vertical plane containing the longitudinal axes of the tool and the wire feed bore to an arbitrary compass direction, thereby enabling the head to be translated rearwardly in that plane to pay out wire in the translation plane from a bond made at a first site on a workpiece by the tool to a second bond site, without requiring that the workpiece be rotated.
Another object of the invention is to provide an automatic ultrasonic wire bonding machine which includes means for translating a bonding tool to an arbitrary location within a defined workspace, and means for rotating the tool to thereby enable wire fixed at one end to a first bond site on a workpiece and at the other end to a supply reel to a pay out through a wire feed bore disposed through the tool at an angle to the longitudinal axis of the tool, the wire remaining in a vertical plane containing the longitudinal and wire bore axes of the tool, thereby enabling the machine to translate the tool in that plane to position the wire above a second bond site on a workpiece, without twisting the wire.
Another object of the invention is to provide an ultrasonic wire bonding machine which includes a cascaded stack of orthogonally translatable support platforms that support an orbital bonding head, the latter supporting a bonding tool, the machine including means for effecting translation motions of the support platforms, and rotation of the orbital bonding head, thereby enabling the ultrasonic bonding tool to be positioned at arbitrary positions within a workspace containing a workpiece, and at arbitrary angular orientations, thus enabling the tip of the bonding tool to be positioned at a first arbitrary bond site location on a workpiece, the tool rotated to align a wire feed bore with a second arbitrary bond site location, and translated thereto to make a second bond, the wire paying out through the wire feed bore without twisting.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
Briefly stated, the present invention comprehends an automatic ultrasonic wire bonding machine which includes an orbital bonding tool support head and automatic means for translating the bonding tool head relative to a workpiece, and independent automatic means for rotating the head, thus enabling a bonding tool tip to form ultrasonic wire bonds at arbitrary locations within a workspace, rotating the tool to desired compass directions, and translating the tool without rotating to a second bond site location. Thus, the ultrasonic wire bonding machine according to the present invention is adapted to bonding wires between arbitrary locations on a workpiece by ultrasonic bonding using a wedge-type ultrasonic bonding tool, without requiring that the workpiece be translated or rotated.
In a preferred embodiment of an automatic ultrasonic bonding machine with orbital bonding tool head according to the present invention, the orbital bonding tool head is supported by a positioning mechanism for translating the bonding tool head, and therefore the tip of an ultrasonic bonding tool, by drive motors to precisely predeterminable positions within a three-dimensional coordinate space containing a workpiece. The positioning mechanism of the wire bonding machine according to the present invention preferably includes a laterally oriented, upper support frame member or gantry, which supports a generally downwardly tiered or cascaded series of linearly translatable support platforms These include a first, upper X-axis tool support platform supported by a first pair of fore-and-aft opposed, front and rear, laterally disposed, parallel linear slide bearings having crossed rollers. This latter pair of bearings enables the Y-axes platform to be translatable in a fore-and-aft Y-axis direction by a Y-axis driver motor.
The first, upper, X-axis tool support platform is translatable in a lateral direction by an X-axis drive motor. The positioning mechanism also includes a second, Y-axis translatable tool support platform which is suspended from the X-axis platform, by a second pair of crossed roller bearings. This pair of bearings consists of two fore-and-aft disposed, laterally opposed parallel linear slide bearings having crossed rollers. This latter pair of bearings enables the Y-axis platform to be translatable in a four-and-aft, Y-axis direction by a Y-axis drive motor.
The positioning mechanism of the wire bonding machine according to the present invention also includes a third, Z-axis support platform which depends downwardly from the Y-axis support platform. The Z-axis support platform is supported from the X-axis platform by a third pair of bearings, consisting of two vertically disposed, fore-and-aft opposed parallel linear slide bearings having crossed rollers. In a preferred embodiment of the machine, the Z-axis support platform bearings are located near front and rear edges of an offset flange plate which depends vertically downwards from a side of the Y-axis supped platform. In an example embodiment, these bearings protrude inwards, i.e., to the right from a flange plate offset to the left side of the Y-axis platform. The Z-axis bearing pair enables the Z-axis platform to be translated in a vertical, Z-axis direction by a Z-axis drive motor.
The orbital bonding head of the automatic ultrasonic wire bonding machine according to the present invention includes a head support assembly which is mounted to a lower front portion of the Z-axis support platform by a cantilever bar which protrudes forward from the Z-axis support platform. The orbital bonding head assembly includes structural components which rotatably support a head that in turn supports an ultrasonic transducer in which is mounted a bonding tool, particularly a wedge bonding tool, and a clamp mechanism for feeding bonding wire through a wire guide bore disposed obliquely through the bonding tool. The orbital bonding tool head includes a four-bar parallelogram linkage support frame which couples an upper portion of the head to the transducer, tool, and wire feed clamp assembly, the four-bar linkage enabling the tool tip to be displaced only vertically in response to a reaction force produced by translating the tool tip downwardly into contact with a workpiece, thus insuring that the tool tip is not displaced laterally and thus avoiding scuffing the workpiece.
Novel features of the orbital bonding tool head include minimization of the weight of rotatable components of the head by locating drive motors for head rotation and clamp actuation rearward of the head, on a non-rotating support arm. Bonding wire is fed to the bonding tool from a supply reel fixed to the Y-axis platform, through a bore concentric with the rotating axis of the head, thus insuring that the bonding wire is not twisted when the head is rotated.
The bonding head is rotatable by an external drive motor coupled by a toothed belt to a spindle-drive sprocket wheel at the upper end of a spindle which supports the head. The head drive motor rotates the head plus and minus 180 degrees, allowing a plane containing the longitudinal axis and wire feed bore axis of the tool to be rotated to any azimuthal direction related to a workpiece.
The orbital head of the bonding machine also includes a clamp actuator drive motor which is coupled to a hollow shaft which fits concentrically inside the head support spindle by a toothed belt which engages a clamp actuator sprocket which is located above the spindle-drive sprocket wheel. Mounted to a lower end of the hollow clamp-drive shaft is a cam wheel which engages a follower coupled by a bell crank assembly to a wire feed clamp, the jaws of which are alternatively openable and closeable onto feed wire in response to pressurization of a pneumatic actuator. Thus, the novel design of the bonding machine according to the present invention enables the wire feed clamp assembly to be operated independently of rotation angle of the head, thereby minimizing the mass of rotating head components by locating the cramp actuator drive motor off of the head.